Free air fan



April-6, 1954 A. G. OSTROGNAI 2,674,407

FREE AIR FAN Filed Dec. 17, 1949 'Invntor-= AllenG. OstI-ognai,

His Attrneg.

Patented Apr. 6, 1954 UNITED STATES PATENT OFFICE FREE AIR FAN New York Application December 17, 1949, Serial No. 133,539

6 Claims.

My invention relates to rotary driven air moving fans and is concerned with the efficient production of desirable air flow in fans operated in free air, that is, not confined by ducts or air guiding housings. More particularly, my invention relates to the design or arrangement of blades in free air fans for the purpose of obtaining unconventional air flow patterns. One object of my invention is to obtain any one of a number of desired forms or patterns of air fiow from a rotary driven fan, using conventional fan blade shapes but without the need of deflectors, baffles, or similar stationary structures which direct or retard the flow. Another object is to promote eificiency of air flow delivery in such a fan driven at a given motor speed, regardless of the size and shape of the pattern of air discharged from the fan. Still another object is to vary the shape of the discharge cone or pattern of air flow of a free air fan of a given design. An additional object is to vary the cone or pattern of air flow while the fan is operating. In these ways the user of my fan is not limited to the normal air flow discharge stream, but various other discharge patterns for direct or indirect air movement may be obtained.

The broad objects of the invention are met by utilizing a primary fan having a set of blades of fixed angle or pitch, and a secondary fan having a set of blades at a different pitch mounted on the same axis as the primary fan. The blades of the primary fan are set at such an angle or pitch so as to draw air toward the blades of the secondary fan, and the blades of the secondary fan throw the air in the desired direction, depending upon the angle of set or pitch. By different relative angles or pitch of the blades of the primary and secondary fans, a choice in the cone or pattern of air flow from the fan may be obtained, varying from a narrow axial stream to a wide radial fiow. According to one aspect of the invention I provide an adjustable means for altering the angle of set or pitch of the blades of the secondary fan so that any one of a number of desired discharge patterns or cones of air flow may be obtained from the same fan assembly. Preferably my invention also includes mechanism for making such alteration of the blade angle or pitch of the secondary fan, and therefore of the discharge cone shape, while the fan continues to operate. Thus, the shape of the cone of air flow may be changed without stopping the fan or the motor driving the fan.

Other objectsand the details of that which I believe to be novel and my invention will be clear from the following description and claims taken with the accompanying drawing in which are shown two examples of a free air fan according to my invention incorporating the primary and secondary blade structure.

In the drawing, Fig. l is a general perspective view of a motor driven fan according to my invention; Fig. 2 is a similar view of a modified form of fan; Fig. 3 is a front view of the hub assembly of the fan of Fig. 1 on an enlarged scale, with certain parts broken away or removed for clarity; Fig. 4 is a sectional view on the line 4-4 of Fig. 3, but with all of the parts in place; Fig. 5 is a similar fragmentary section, but on the line 5-5 of Fig. 3; Fig. 6 is a plan view of the parts shown in Fig. 3, and Fig. 7 is a series of diagrams indicating by arrows the air flow through a fan like the fan of Fig. 2 with various relative settings of the primary and secondary blades.

Because the basic principles of construction and operation of my invention will be more easily understood by reference to the form of Fig. 2 of the drawing, this form will be explained first, although the form of Fig. 1 will probably be preferable from a commercial standpoint because of its similarity in appearance to more conventional fans.

Referring to Fig. 2, the fan may include a housing I for the electric motor or other power source (not shown) and suitable electrical or other power connections, as will be obvious. The motor housing is carried on a base or support 2 in any suitable manner. Extending from the motor housing is a rotatable shaft 3, driven by the motor or other power source. Driven by the motor shaft is a primary fan, shown as a set of individual axial flow type fan blades d, and a secondary fan, shown as a set of similar individual blades 5, mounted in tandem with the first blades.

Although I have shown the fan blades as extending in vertical planes, and rotating about a horizontal motor shaft axis, it should be obvious that a vertical axis of rotation or any intermediate axial angle could be used if desired, and the fan motor housing could be adjustably or fixedly mounted in any convenient manner to accomplish the desired axial inclination.

As stated earlier, the primary fan blades are given a fixed pitch or angle so that they will draw air to the total fan assembly and direct it toward the secondary fan blades. Explanation of the operation will be clear by reference to the diagrams of Fig. '7. The primary fan is given a "normal pitch, directing air toward the secondary. The secondary fan; depending upon its pitch, will either assist the flow of air from the primary blades, disperse it, or oppose it. If the pitch of the secondary blades is set so as to correspond to the normal pitch of the primary blades, the secondary blades will assist the air flow from the first blades and the air will leave the fan in a more or less conventional manner in a narrow stream, as shown at A in Fig. '7.

This may be called normal fan operation. However, if the secondary blades are mounted at an angle or pitch different from the primary blades then the normal pattern of air flow no longer exists.

If the secondary blades are depitched slightly, the secondary fan cannot handle all of the air supplied to it by the primary fan. In this case, the primary fan tends to rotate the secondary fan, with a decrease in air velocity and with a proportional increase in the area of air flow. Thus, when the pitch of the secondary blades is decreased, the area of the cone of air flow is increased as shown at B in Fig. 7.

When the secondary blade pitch is further decreased, this fan becomes in effect flat, and acts much as a deflector. The air flow from the primary blades will try to bypass the secondary blades and will leave the fan in a wide cone to clear the periphery of the secondary blades as shown at C in Fig. '7.

As the pitch of the secondary blades is changed beyond the flat position, the secondary blade pitch will become reversed with respect to the primary blade pitch and the two fans will tend to buck one another with the resultant air flow leaving in a more or less radial direction as shown at D in Fig. 7, depending upon the amount of pitch on the secondary blades.

In the form of Fig. 2, with the various relative blade positions explained in Fig. 7, it is assumed that the primary and secondary blades are mounted in tandem at opposite ends of the same motor shaft, to rotate in planes parallel to but spaced from each other. However, it has been found that much the same effect may be produced by making the planes of rotation of the primary and secondary blades extremely close to each other, or even coincident with each other, so that both sets of blades may be mounted on one end of a motor shaft as shown in Fig. 1. Because this is the preferred form, the remaining structure will be described in connection with this form, although obviously much of the same structure could be used with a fan according to Fig. 2.

When it is desired to produce a fan having air flow characteristics of an unconventional or abnormal nature such as the air flow in B, C or D of Fig. 7, or any intermediate pattern, the primary blade or blades are given a pitch of normal" inclination as explained above, and the secondary blade or blades are given a different pitch, which is determined by the desired pattern or cone to be produced. This different pitch of the secondary blades may be obtained by permanently mounting them in their desired angular relation with respect to the motor shaft, but it is usually preferable to provide an adjustable means for mounting the secondary blades so that a given fan is not limited in the particular cone or pattern of air flow which it may produce. Furthermore, it is desirable that adjustment of the pitch of the secondary blades can be made while the fan is operating or rotating. The following description will show one way in which this may be accomplished.

Referring to Figs. 1, 3, 4, 5 and 6 of the drawing, the motor shaft 3 has a hub frame 6 secured on its end as by a central bore '1 in the frame, which extends over the motor shaft, and a set screw 8 passing through the frame into the bore and bearing against the shaft. The hub frame carries all of the blades and also the mechanism for changing the pitch of the secondary blades. For holding the primary blades 4, I have shown rearwardly extending shoulders or ears 9 at the circumference of the hub frame, these having suitable bores in which blade shafts III are held, as by means of set screws II. The blades may be secured to the blade shafts in any desirable way, such as by rivets l2 which pass through the blades into the shafts. This same construction may be used to secure the secondary blades adjustably with respect to the pitch or set of the primary blades, but this type of mounting does not lend itself to easy adjustment, and such adjustment cannot be made while the fan is rotating. Therefore, I have shown another mechanism which is preferred for obtaining adjustment of the secondary blades during fan rotation.

Between each of the shoulders or ears 9 in the circumference of the hub frame are similar rearwardly extending ears !3 which are provided with bores I4 rotatably receiving blade shafts 5 for the secondary blades 5. As before, the blades may be secured to the shafts in any suitable manner. I have shown rivets 16.

In order to prevent the primary and secondary blades from flying away from the hub frame by centrifugal force when the fan is rotated, I provide means such as the blade shaft bearing pin l1 (bottom of Fig. 4) which extends through the blade shaft and bears against the inner face of the ear [3. Other convenient arrangements could be used, such as snap retaining rings around the fan blade shafts, like the snap ring l9 which will be described below.

Because the blade shafts 15 are rotatable within the bores I4, some means must be provided to hold the blade shafts in desired positions of adjustment, and to insure that the pitch of each of the individual secondary blades is the same at any degree of adjustment. For this purpose I provide a series of blade positioning discs l8 which rotatably seat around the hub frame outside of the motor shaft bore 1. On one side, this stack of positioning discs is held by a snap ring I9 which seats in a groove 20 in the hub frame. On the other side the positioning discs are held by a friction-producing spring 2| which bears between the discs and the back face of the hub frame. This normally holds the disc against rotation with respect to the hub frame.

Provided around the periphery of the blade positioning discs are a series of slots or notches 22, generally located opposite the base of each of the fan blade shafts l5. Fixed to and extending from each of the blade shafts is a blade positioning pin 23 which seats in corresponding slot 22 of the blade positioning discs. It will thus be seen that if one of the shafts I5 is rotated, the angular position of its blade positioning pin 23 will change, and this will move the positioning discs, through the slots 22 and con sequently move all of the other blade shafts through an equal angle. Therefore, if the adjustment mechanism rotates one of the secondary blades, all of the blades will be moved through similar angles at the same time.

In order to accomplish the rotation of the blade shafts for the adjustment of secondary blade pitch while the fan is operating, I have provided a hub cap or knob 24 at the front of the fan which may be manually grasped or retarded while the fan is operating. Normally this knob rotates at the same speed as the motor shaft because of friction between the various parts of the assembly, assisted by the friction producing spring 2| described above. However, when the knob is grasped or retarded and the motor shaft continues to operate, a suitable gear mechanism will change the angle of pitch of the secondary blades. In the form shown, this gear mechanism includes the worm 25 fixed to the shouldered driving pin 26 and rotatably mounted in the hub frame as by the bearing block 21. The driving pin is extended forwardly into a suitable recess 28 in the hub cap and the hub cap is held in place by a set screw 29, accessible through an opening 30 in the cap. The worm is thus fixed with relation to the cap. At one side of the worm 25 the hub frame rotatably carries a worm wheel 3! which engages with the worm and which carries and drives a pinion and bearing shaft 32 to which a pinion 33 is secured. This pinion in turn engages and drives a gear 34, rotatably mounted on the frame as by the countersunk screw 34a. Gear 34 carries a bladedriving pin 35, the position of which governs the position of the blades. This is accomplished through the blade positioner element 36 which lies against the face of the gear 34 and is provided with a slot 31 in which the driving pin may slide. The slotted blade positioner element extends through a hole 38 in the hub frame and is secured to the base of one of the fan shafts l5 at a point opposite its blade positioning pin 23. In the form shown, the blade positioning pin and the slotted blade positioner are shown as parts of the same piece, both being secured to one of the blade shafts.

The above arrangement operates as follows: When the fan is rotating and it is desired to change the pitch of the secondary blades, the user grasps the knob 24 or retards it by suitable finger pressure, and this stops the worm 25' from rotating in unison with the rotating motor shaft 3. Because the hub frame continues to rotate with the motor shaft, this has the effect of driving the worm with respect to the rest of the gear mechanism. The worm will therefore drive the worm wheel, which drives the pinion, rotating the gear 34 and changing the position of the blade driving pin 35. As this pin slides in the slot 31 it will move the blade positioner from side to side and vary the angle or pitch of the blade. As explained above, a change in the pitch of one blade will make a corresponding change in the pitch of the other blades through engagement of the blade positioning pins with the slots in the discs 18. By holding or retarding rotation of the knob 24 for the proper time, any desired air cone pattern may be obtained while the fan is rotating, and changes in the cone may be made at will. When the fan is stopped, adjustment of the blade pitch may be made by twisting the knob. However, this may be laborious because the gear ratio is designed to produce a fairly slow rate of pitch change when the knob is held stationary and the fan is rotating at high speed.

I have shown a hub ring 39 covering the space between the hub cap 24 and the hub frame 6, and secured as by means of screws 40 threaded 6 into the hub frame. This hub ring is desirable from an appearance standpoint and to keep out dirt, but it may be eliminated entirely or obviously combined with and made a part of either the hub frame or the hub cap.

I have also shown a counterweight 4| on the hub frame which will tend to balance the gear mechanism on the frame and prevent excessive vibration.

Although the fan blades illustrated are quite flat and simple in form, it is understood that this need not be so. The blades may be given any of the usual curvatures or outlines found desirablein free air fans of more conventional types, as long as the blade shape does not interfere with proper operation according to my invention. See the blade shapes in Fig. 7. For instance, the primary and secondary blades are shown as of the same size and design and of an equal number. The number-of blades in each set has no real significance apart from practical considerations, and obviously the shape of the primary blades could be quite different from that of the secondary blades without affecting proper functioning of the fan.

When the primary fan blades are spoken of as of normal pitch, this means normal both for the fan of this invention and as compared to conventional or known axial flow type free air fans. Usually such fan blades are mounted at an angle of about 45 from the axial line of the fan at the blade base, and often are twisted or curved from this angle to a greater angle toward the blade tip. The blade tips may also be extended at their trailing edges, as is usual in some known designs. As stated above, the role of the primary fan structure is to draw air to the secondary fan blade or blades.

The secondary blades may be given shapes similar to the primary blades, but for ease in manufacture as well as for best results when mounted for variable pitch, these blades should be kept fairly simple in design. Shapes which exhibit extraordinary changes in comparative eificiency when mounted at different pitch angles should be avoided in this case. The secondary blade structure delivers or discharges air fed to it by the primary system.

Protective guards (not shown) may be provided around the fan blades. These need not differ from present guards, ordinarily made in the form of an open cage of wire, excepting for the provision of a suitable clearance opening through which the knob 24 freely projects, when this knob is to be used.

As will be evident from the foregoing description, certain aspects of my invention are not lim ited to the particular details of construction of the examples illustrated, and I contemplate that various and other modifications and applications of the invention will occur to those skilled in the art. It is therefore my intention that the appended claims shall cover such modifications and applications as do not depart from the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a free air fan of the type having a motor and a rotary shaft driven by said motor, that improvement which comprises a first set of axial flow type fan blades fixed at normal pitch on said shaft to rotate therewith, a second similar set of axial flow type fan blades of variable pitch fixed near said first set on said shaft to rotate with said shaft, a manually engageable hub ro- 7. tatably mounted on said shaft near said second blade set, and a pitch-changing mechanism connected between said hub and the fan blades of said second blade set, actuated by relative rotation between said hub and said shaft to change the pitch of the blades in the second set.

2. In a free air fan of the type having a driving motor, and a rotary shaft driven by the motor with ends extending at both ends of the motor, that improvement which comprises a first set of fan blades fixed at normal pitch on one end of said shaft to rotate therewith, a second similar set of fan blades fixed on the other end of said shaft to rotate therewith, but movable in pitch, a manually engageable knob rotatably mounted on said other end of said shaft near said second set of blades, and a gear train between said knob and said second set of fan blades actuable to change the pitch of said blades upon relative rotation between said shaft and said knob.

3. In a free air fan of the type having a driving motor and a rotary shaft driven by the motor with an end extending from the motor, that improvement which comprises a first set of fan blades fixed at normal pitch on said shaft end to rotate therewith, a second similar set of fan blades of variable pitch on said shaft in the same plane of rotation as said first set, a hub member rotatably mounted on said shaft near said blade sets, and pitch-varying mechanism connected cetween said hub and the fan blades of said second set, actuable to vary the pitch of the blades in the second set upon relative rotation between said hub and said shaft.

4. In a free air fan of the type having a driving motor and a rotary shaft driven by the motor, that improvement which comprises an axial flow type primary fan blade of fixed pitch coaxially mounted on said shaft and rotatable therewith,

an axial flow type secondary fan blade of varia- I ble pitch coaxially mounted on said shaft similar to the primary blade and rotatable with the shaft in unison with the primary blade at the same speed and in the same direction, means ad- 8: justably mounting said secondary blade on said shaft to vary the pitch position of said blade, and means for selectively fixing said secondary blade in any of its adjusted pitch positions.

5. In a free air fan of the type having a driving motor and a rotary shaft driven by the motor, that improvement which comprises a primary fan blade of fixed pitch coaxially mounted on said shaft and rotatable therewith, a secondary fan blade of variable pitch coaxially mounted on said shaft similar to the primary blade and rotatable with the shaft in unison with the primary blade at the same speed and in the same direction, means adjustably mounting said secondary blade on said shaft to vary the pitch of the secondary blade with respect to the pitch of the primary blade, and means operable during fan rotation for selectively changing the pitch of said secondary blade.

6. In a free air fan of the type having a driving motor and a rotary shaft driven by the motor, that improvement which comprises a primary set of axial flow type fan blades fixed to rotate with said shaft at normal pitch, a secondary set of axial flow type blades similar to said primary blades and also fixed to rotate with said shaft but at variable pitch, means adjustably mounting said secondary blades on said shaft to vary the pitch toward and away from normal pitch, and manually operable means carried entirely by said extended shaft for selectively altering the pitch of said secondary blades, said pitchaltering means being manually engageable and operable while said shaft is rotating.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 807,498 Roper Dec. 19, 1905 811,287 Gray Jan. 30, 1905 1,925,156 Vaughn Sept. 5, 1933 1,946,571 Briner Feb. 13, 1934 2,088,255 Adams July 27, 1937 2,276,663 Mercier Mar. 17, 1942 

